CHENNAI DISTRICT
UNIT TEST I
CLASS: XII MAX. MARK: 35
SUBJECT: PHYSICS TIME: 1 hr. 30 min
PART -A
Answer all the questions. 5 × 1 = 5
1. Which charge configuration produces a uniform electric field?
(a) point charge
(b) uniformly charged infinite line
(c) uniformly charged infinite plane
(d) uniformly charged spherical shell
2. An electric dipole is placed at an alignment angle of 30o with an electric field of 2 × 105
N C–1
. It
experiences a torque equal to 8 N m. The charge on the dipole if the dipole length is 1 cm is
(a) 4 mC
(b) 8 mC
(c) 5 mC
(d) 7 mC
3. Two identical conducting balls having positive charges q1 and q2 are separated by a centre-to-
centre distance r. If they are made to touch each other and then separated to the same distance, the
force between them will be
(a) less than before
(b) same as before
(c) more than before
(d) zero
4. Two points A and B are maintained at a potential of 7 V and - 4 V respectively. The work done in
moving 50 electrons from A to B is
(a) 8.80 × 10–17 J
(b) -8.80 × 10–17 J
(c) 4.40 × 10–17 J
(d) 5.80 × 10–17 J
5. A parallel plate capacitor stores a charge Q at a voltage V. Suppose the area of the parallel plate
capacitor and the distance between the plates are each doubled then which is the quantity that will change?
(a) Capacitance
(b) Charge
(c) Voltage
(d) Energy density
PART -B
Answer any three questions. (Question number 10 is compulsory) 3 × 2 = 6
6. Write down Coulomb’s law in vector form and mention what each term represents.
7. Define ‘electric dipole’.
8. Define ‘electrostatic potential energy’.
9. What is corona discharge?
10. Calculate the number of electrons in one coulomb of negative charge.
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PART-C
Answer any three questions. 3 × 3 = 9
11. Discuss any two basic properties of electric charges.
12. What are the differences between Coulomb force and gravitational force?
13. Derive an expression for electrostatic potential due to a point charge.
14. Obtain an expression for potential energy due to a collection of three-point charges which are
separated by finite distances.
15. Obtain the expression for capacitance for a parallel plate capacitor.
PART-D
Answer any three questions. 3 × 5 = 15
16. Calculate the electric field due to a dipole on its axial line.
17. Derive an expression for the torque experienced by a dipole due to a uniform electric field.
18. Obtain the expression for electric field due to a charged infinite plane sheet.
19. Derive the expression for resultant capacitance, when capacitors are connected in series and in
parallel.
20. Explain in detail the construction and working of a Van de Graaff generator.
